Among color recording methods, inkjet printing is one of the typical ones. So far, varieties of ink jetting methods have been developed to form fine ink drops which will be adsorbed on recording materials (e.g., paper, film, fabric, etc.) to achieve the purpose of recording. As the nozzles do not contact the recording materials, so ink jet printers are characterized by quietness as well as ease in realizing miniaturization, high-speed and colorization. Therefore, ink jet printing has been developed rapidly in recent years.
Traditional inks are prepared as follows: Water-soluble dyes are dissolved in aqueous media and water-soluble organic solvents capable of preventing inks from blocking nibs are added to prepare inks for fountain pens and brush pens. Different from traditional inks, inkjet inks requires to be capable of forming high-density images, not blocking nozzles, drying well, bleeding little and being stored stably. In addition, images formed by ink-jet inks must be of water resistance, light resistance, moisture resistance, ozone resistance, solubility, and fastness of these properties.
When applications of ink-jet printers expand from small printers to industrial large printers, higher requirements are raised for fastness of water resistance, moisture resistance, light resistance and gas resistance. Water resistance: Usually the substrate surface may adsorb porous silicon oxide, cationic polymers, alumina sol or special ceramics, and thus if dyes are applied on paper surface together with such organic or inorganic particles as well as PVA resin, water resistance can be significantly improved. Light resistance: In the four primary colors, namely yellow, magenta, cyan and black, magenta has the weakest light resistance and can seriously affect image quality; therefore, it has become an important subject to improve light resistance of magenta dyes. Moisture resistance: If printed images are to be saved in a high-humidity environment, it is required that dyes, as part of recording materials, are of good anti-bleeding fastness. If bleeding of dyes occurs, image quality will be significantly reduced, especially on occasions that high requirements are imposed on colour matching for photos. However, compared with water resistance, improvement of light resistance, moisture resistance, ozone resistance and solubility are more difficult to be realized
In addition, with the wide popularity of digital cameras in recent years, the opportunity to print photos at home is increasing. In saving printed products, oxidizing gases in indoor air which causes discoloration of images has also become one of the problems. Oxidizing gases cause discoloration and fading of images by reaction with the dyes on or in the recording paper. Particularly, ozone gas is one of the main materials of promoting oxidization and fading of inkjet printed images, so the improvement of ozone gas resistance has become a subject equally important as the improvement of light resistance.
Typical examples of magenta dyes for inkjet inks include: xanthene type rhodamine dyes and azo dyes derived from H-acid coupling. While rhodamine dyes are most prominent in tone and brightness, they are extremely poor in light resistance. H-acid derived azo dyes are of good lustre and water resistance and meanwhile are of poor light resistance, ozone resistance and brightness; particularly compared with cyan dyes with copper phthalocyanine as the representative and yellow azo dyes, it is still of poor light resistance.
In recent years, magenta dyes of outstanding light resistance have been developed, including anthrapyridone dyes. They have no sulfonic groups on their molecular scaffolds, indicating advantages of brightness, light resistance, ozone resistance, etc.
Examples include patents of Fuji Photo Film: JP2007138124A, JP2007224119A, CN101370882A, WO2009044094A2, US2010080908A1, GB2464188A; patents of Canon: US2002041318A1, US2002036681A1, JP2002069349A, JP2006199922A, CN101298526A, US2007242100A1, US2005057607A1; patents of Epson: US2005115458A1, US2005115459A1, US2007263055A1, US2008257209A1; patents of Avecia: U.S. Pat. No.6,183,549B1, and GB2353533A; Patents of Nippon Kayaku Co., Ltd.: EP0927747A1, JP2000109464A, JP2000191660A, U.S. Pat. No. 6,471,760B1, JP2002332419, U.S. Pat. No. 6,648,952B1, US2004134383A1, EP1626070A1, US2006219131A1, WO2009116243A1, CN101547976A, US2010015410A1 (2010 Jan. 21); Patents of ILFORD: US2010075047A1, etc.
However, dyes revealed in these patents do not meet all requirements of tone, brightness, light resistance, water resistance, ozone resistance as well as solubility and solution stability. Although some improvements in light resistance and ozone resistance have been made in some dyes, the solubility of the dyes and the long-term stability of inkjet inks are still insufficient. Particularly, long-term stability of dyes in inks is associated with their solubility; In many cases, solubility of dyes in water is not ideal, and it is unavoidable to replace M with Li to improve the solubility within a limited range.